A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In the conventional lithographic apparatus, a patterning device handling apparatus is provided to exchange a patterning device between the patterning device support on which the patterning device is positioned during the transfer of a pattern on a substrate, and a stationary loading station wherein one or more patterning devices can be placed. The patterning devices are exchanged between the loading station and the patterning device station to subsequently transfer the different patterns of the patterning devices on the substrates which are placed on a substrate support.
Production capacity of a lithographic apparatus is, in part, affected by the exchange time needed to take away a patterning device which is located on the patterning device support and place another patterning device on the patterning device support. During the time needed for this exchange, no pattern can be transferred on a substrate. In order to increase the capacity of the lithographic apparatus it is desirable to decrease this exchange time.
In order to keep the exchange time small, the patterning device handling apparatus of a conventional lithographic apparatus includes a turret and a robot. The turret can hold at the same time two patterning devices in two different holding positions, whereby the turret can be rotated around its vertical axis so that one of the two holding positions can be turned to a position wherein the turret can exchange a patterning device with the patterning device support. In another position, usually when the turret is rotated over 180 degrees, a patterning device in the other of the two holding position can be exchanged with the patterning device support.
The patterning device handling apparatus further includes a robot to exchange a patterning device between a loading station and the turret, so that a patterning device held by the turret can be exchanged for another one.
When a first patterning device held in the patterning device support is to be exchanged by a second patterning device which is placed in a loading station, the second patterning device can, during the transfer of the pattern of the first patterning device on a substrate, be placed by the robot in one of the holding positions of the turret. When the transfer is finished, the first patterning device is taken by the turret out of the patterning device support. After that, the turret is rotated and the second patterning device can then be placed on the patterning device support. Subsequently the pattern can be transferred on a substrate. During this pattern transfer the robot can take the second patterning device out of the turret and place it in a loading station.
However, the turret is a relative expensive part of the lithographic apparatus, also due to the required position of the turret close to the patterning device support.